Abstract:To assess the impact of thinning intensity on soil nutrient release characteristics, the Daling Mountain Forest Farm in Dongguan City, Guangdong Province was selected as the study area. Soil carbon (C), nitrogen (N), and phosphorus (P) contents, as well as the extracellular enzyme activities related to N and P nutrient acquisition, were measured in 13- to 17-year-old Acacia mangium and Eucalyptus urophylla plantations that had undergone near-natural transformation (thinning + planting native tree species) under three thinning intensities (no thinning, 30% thinning, and 60%–70% thinning). The results showed that compared with the unthinned plots, the available N and P contents in the thinned plots of A. mangium increased by an average of 28% and 71%, respectively, and those in the thinned plots of E. urophylla increased by an average of 21% and 33%, respectively. The activities of soil C, N, and P acquisition enzymes in both thinned plots decreased to varying degrees. By comparing the stoichiometric ratios and vector characteristics of ecological enzymes under the two thinning intensities, it was indicated that thinning could effectively alleviate the C limitation required for nutrient transformation, but excessive thinning might further lead to soil N limitation. It was suggested that moderate thinning (30%) could balance the release of N and P nutrients in the soil and the improvement of vegetation diversity in both plantations, and should be the optimal choice for thinning intensity in the near-natural transformation of these two forest types.
